The invention relates to a circuit arrangement for activating sensors and evaluating their signals, in particular for parametric sensors with complex impedances, the circuit arrangement comprising at least one sensor for acquiring mechanical quantities. The invention further relates to a method for activating sensors and evaluating their signals, in particular parametric sensors with complex impedances, wherein at least one sensor acquires mechanical quantities.
Circuit arrangements for activating sensors and evaluating their signals have been known from practice for a long time. Known circuit arrangements for activating sensors and evaluating their signals with complex impedances, for example, differential and nondifferential, inductive or capacitive sensors, such as linear variable-differential transformers (LVDT), differential chokes, eddy current sensors, or the like, make use of a bridge circuit, in general an alternating-current bridge circuit, which is supplied by a sinusoidal oscillator. After amplification by an ac amplifier, the output voltage of the ac bridge circuit is rectified with a phase-sensitive demodulator, and after the required filtration, the thus-obtained dc voltage, which is approximately proportional to the measured quantity, is converted with an A/D converter into a corresponding digital signal.
Circuit arrangements of this type are problematic, in particular to the extent that they make great demands on all structural elements of the circuit arrangement. For example, the sinusoidal oscillator must exhibit a satisfactory stability in amplitude, frequency, and phase, the phase-sensitive demodulator a satisfactory linearity, and the circuit arrangement in general a very satisfactory temperature- and long-term stability. Furthermore, the very complicated layout of the circuit arrangement is a problem. These two aspects together are the reason for the often very high price of such a circuit arrangement, which remains high, even when the circuit arrangement is made as an integrated component in large quantities.
The known circuit arrangements are also problematic to the extent that the technical properties are often subjected to considerable limitations by the occurrence of phase shifts, phase rotations, and nonlinear distortions of the bridge output voltage, which often prevail as a result of the complex impedances of the sensor, and by the occurring nonlinearities of the unbalanced bridge circuit. Thus, for example, higher harmonics that are generated by nonlinear effects in the ferromagnetic circuit of the sensor, and the quadrature component limit the resolution of the entire arrangement.
DE 39 10 597 A1 discloses a circuit arrangement with a sensor and a method for activating sensors and evaluating their signals, wherein the sensor comprises a coil, and wherein the temperature-dependent inductance fluctuations of the coil undergo a compensation. In this arrangement, the ohmic resistor of the coil forms a temperature measuring sensor. The acquisition of the quantity being measured, for example, a distance, and the temperature proceeds in two separate circuits, which are controlled by a microcomputer. Consequently, the circuit arrangement disclosed in DE 39 10 597 A1 has all the above-described disadvantages.
It is therefore an object of the present invention to describe both a circuit arrangement and a method for activating sensors and evaluating their signals of the initially described type, which allow to minimize or largely prevent temperature-caused disturbances with a constructionally simple layout.